In the following, the term “plethysmography” (and its derivative words) means measurement of a cross-sectional area of the body, such as a cross-sectional area of the chest or of the abdomen, or a body part, such as a cross-sectional area of the neck or of an arm. (This meaning is somewhat more limited than is standard in the medical arts.) Further, the phrase “inductive plethysmography” means herein plethysmographic measurements which depend on inductance determinations.
Measurement of pulmonary and cardiac physiological parameters by means of inductive plethysmography is known. For example, many measurement methods and apparatus are disclosed in the following U.S. patents, the entire disclosures of which are incorporated herein, in their entireties, by reference, for all purposes.
(1) The '872 patent: U.S. Pat. No. 4,308,872, issued Jan. 5, 1982 and titled “Method and Apparatus for Monitoring Respiration,” discloses a method and apparatus for monitoring respiration volumes by measuring variations in the patient's chest cross sectional area, or variations in both chest and abdomen cross sectional areas, each area being measured by determining the inductance of an extensible electrical conductor closely looped around the body, and the measurements being calibrated by measuring the area variations for a few breaths while directly measuring corresponding volumes of breath, preferably while the patient assumes at least two body positions, for example sitting and supine.
(2) The '534 patent: U.S. Pat. No. 4,373,534, issued Feb. 15, 1983 and titled “Method and Apparatus for Calibrating Respiration Monitoring System,” discloses methods and systems in which respiration volume is determined by weighting signals representing abdominal and chest cross-sectional areas, where the weighting factors are determined by a procedure involving measuring respiration volume by an alternate measuring apparatus along with unweighted chest and abdomen signals, the measurements occurring for a first series of breaths based with a first relative chest and abdominal contribution and for a second series of breaths based on a second relative chest and abdominal contribution.
(3) The '252 patent: U.S. Pat. No. 4,452,252, issued Jun. 5, 1984 and titled “Non-invasive Method for Monitoring Cardiopulmonary Parameters,” discloses a method for monitoring cardiopulmonary events by inductive plethysmographic measurement of a cross-sectional area of the neck, and further discloses a method for monitoring mouth volume by inductive plethysmographic measurement of a cross-sectional area of the head in a plane which extends through the mouth.
(4) The '015 patent: U.S. Pat. No. 4,456,015, issued Jun. 26, 1984 and titled “Non-invasive Method for Semiquantitative Measurement of Neck Volume Changes,” discloses a method of plethysmographic measurement of a subject's neck volume by providing an extensible conductor closely circling the neck and, first, calibrated against cross-sectional area so that neck volume may be determined from the conductor's inductance, and also, second, calibrated against invasively-measured intrapleural pressure so that the intrapleural pressure may also be determined from the conductor's inductance, and also so that intrapleural pressure may also be obtained from measured neck volume.
(5) The '407 patent: U.S. Pat. No. 4,648,407, issued Mar. 10, 1987 and titled “Method for Detecting and Differentiating Central and Obstructive Apneas in Newborns,” disclosing methods for detecting the presence and origin of apnea in newborns by concurrently monitoring relative movement of the cranial bones (which have been found to move with respiration as a function of intrapleural pressure), preferably by a surface inductive plethysmographic transducer, and nasal ventilation, preferably by a nasal cannula, thermistor, thermocouple or CO2 sensor, wherein absence of changes in both cranial bone movement and respiratory air flow at the nose indicates of the presence of central apnea, while absence of nasal air flow accompanied by continuing cranial bone movements indicates of obstructive apnea.
(6) The '962 patent: U.S. Pat. No. 4,777,962, issued Oct. 18, 1988 and titled “Method and Apparatus for Distinguishing Central Obstructive and Mixed Apneas by External Monitoring Devices Which Measure Rib Cage and Abdominal Compartmental Excursions During Respiration,” discloses an apparatus and method for distinguishing between different types of apneic episodes. The method includes measuring a new index, Total Compartmental Displacement/Tidal Volume (TCD/VT), and measuring the phase relation between the abdominal and rib cage contributions to total respiration volume, wherein an episode is classified as central, obstructive or mixed based on the value of TCD/VT and the phase relation.
(7) The '640 patent: U.S. Pat. No. 4,807,640, issued Feb. 28, 1989 and titled “Stretchable Band-type Transducer Particularly Suited for Respiration Monitoring Apparatus,” discloses an improved, low-cost stretchable band incorporating a conductor for disposition about the human torso or other three dimensional object, and particularly intended for use with respiration monitoring by means of inductive plethysmography, a method for making the band, which method is suitable to mass production techniques, and an improved enclosure housing circuitry releasably connected to the conductor in the band when the band is incorporated in respiration monitoring apparatus.
(8) The '473 patent: U.S. Pat. No. 4,815,473, issued Mar. 28, 1989 and titled “Method and Apparatus for Monitoring Respiration,” discloses a method and apparatus for monitoring respiration volumes by inductive plethysmographic measurement of variations in a patient's chest cross sectional area, or preferably, variations in both chest and abdomen areas during breathing, and a method for calibrating such an apparatus by measuring cross-sectional area variations for a few breaths while directly measuring corresponding volumes of breath, preferably while the patient assumes at least two body positions, for example sitting and supine.
***(9) The '766 patent: U.S. Pat. No. 4,860,766, issued Aug. 29, 1989 and titled “Noninvasive Method for Measuring and Monitoring Intrapleural Pressure in Newborns,” discloses measuring intrapleural pressure of a newborn subject by detecting relative movement between adjacently-proximate cranial bones, preferably, using a surface inductive plethysmographic transducer secured on the subject's head across at least two adjacently-proximate cranial bones, and a method of calibrating such measurements by temporarily manually occluding the subject's nose or, if intubated, the endotracheal tube, to measure the airway pressure during such occlusion as the subject makes an inspiratory effort and comparing the measured pressure to the measured signal.
(10) The '109 patent: U.S. Pat. No. 4,834,109, issued May 30, 1989 and titled “Single Position Non-invasive Calibration Technique,” discloses an improved method for calibrating inductive plethysmographic measurement of respiration volume by totaling, during a period of breathing, a plurality of values of a parameter indicative of the relative amplitude, for each breath, of uncalibrated rib cage and abdomen signals, and by dividing the average variability of the means of the total of the values of one of the rib cage and abdomen signals by the average variability of the mean of the total of the values of the other signal, the quotient being so derived represents a signal weighting factor for determining respiration volume.
(11) The '277 patent: U.S. Pat. No. 4,986,277, issued Jan. 22, 1991 and titled “Method and Apparatus for Non-invasive Monitoring of Central Venous Pressure,” discloses a method and apparatus for measuring central venous pressure (CVP) and changes in CVP along with an improved transducer (50) for measuring CVP in infants, wherein a plethysmographic transducer is disposed on the neck of a subject (or on the head in the case of infants), the signal from the transducer is processed to obtain a cardiac component, and the vertical distance from the transducer to a reference level is adjusted until a position is located at which the signal changes between a venous configuration and an arterial or mixed venous-arterial configuration, at which position the vertical distance approximates CVP.
(12) The '540 patent: U.S. Pat. No. 5,040,540, issued Aug. 20, 1991 and titled “Method and Apparatus for Non-invasive Monitoring of Central Venous Pressure, and Improved Transducer Therefor,” discloses an improved method and apparatus for measuring central venous pressure (CVP), and changes in CVP, along with an improved transducer for measuring CVP in infants.
(13) The '935 patent: U.S. Pat. No. 5,159,935, issued Nov. 3, 1992 and titled “Non-invasive Estimation of Individual Lung Function,” discloses a non-invasive method and apparatus for plethysmographic monitoring individual lung function by disposing a transducer on the torso above the lung to be monitored, the transducer producing a signal corresponding to movement of the torso portion there beneath which, in turn, corresponds to changes in the volume of the underlying lung, and also a method and apparatus for monitoring regional lung volume changes by utilizing transducers positioned on the torso to encompass only a portion of the underlying lung.
(14) The '151 patent: U.S. Pat. No. 5,178,151, issued Jan. 12, 1993 and titled “System for Non-invasive Detection of Changes of Cardiac Volumes and Aortic Pulses,”, discloses a method and an apparatus therefor for monitoring cardiac function in an animal or human subject including the steps of placing a first movement detecting transducer on the torso, said transducer overlying at least part of two diametrically opposed borders of the heart or great vessels; generating a signal indicative of the movement of the torso portion subtended by the transducer, said signal including a cardiac component comprising at least a segmental ventricular volume waveform or a segmental aortic pressure pulse waveform and assessing cardiac function by monitoring changes in said ventricular volume waveform or said aortic pressure pulse waveform.
(15) The '678 patent: U.S. Pat. No. 5,301,678, issued Apr. 12, 1994 and titled “Stretchable Band-Type Transducer Particularly Suited for Use with Respiration Monitoring Apparatus,” an improved, low-cost stretchable band incorporating a conductor for disposition around the human torso or other three-dimensional object, and particularly intended for use with plethysmographic respiration monitoring apparatus, is disclosed.
(16) The '968 patent: U.S. Pat. No. 5,331,968, issued Jul. 26, 1994 and titled “Inductive Plethysmographic Transducers and Electronic Circuitry Therefor,” discloses an apparatus and method for improving the detection of the inductance “signal” generated by an inductive plethysmograph by modifying the design of the inductive plethysmograph and also by improving the design of the associated circuitry, both of which permit the associated circuitry may be located remotely rather than on the transducer, the improvement including selecting the impedance matching transformer joining an inductive plethysmograph to an oscillator such that the inductance of its primary winding is greater than about ten times the reflected inductance of the inductive plethysmograph and the cable joining it to the transformer, or circling the conductor of the inductive plethysmograph therein around the relevant body portion a plurality of times, or selecting the cable connecting the inductive plethysmograph to the transformer such that the ratio of the diameter of its screen to the diameter of its center conductor is minimized for reducing the inductance per unit length thereof.
(17) The '425 patent: U.S. Pat. No. 5,588,425, issued Dec. 31, 1996 and titled “Method and Apparatus for Discriminating Between Valid and Artifactual Pulse Waveforms in Pulse Oximetry,” discloses a method and apparatus for use in pulse oximetry for discriminating between valid pulse waveforms, determined with a photoelectric plethysmograph, from which arterial oxygen saturation levels are accepted, and artifactual pulse waveforms, from which saturation levels are rejected, according to whether the systolic upstroke time of each pulse waveform is within a predetermined range, it having been discovered that systolic upstroke times for valid pulse waveforms are in a consistent, narrow range which varies only slightly from subject to subject and which may be defined empirically for each subject or established by a default setting applicable to all subjects,
(18) The '388 patent: U.S. Pat. No. 6,015,388, issued Jan. 18, 2000 and titled “Method for Analyzing Breath Waveforms as to Their Neuromuscular Respiratory Implications,” discloses a method for measuring respiratory drive by determining a peak inspiratory flow and a peak inspiratory acceleration from a breath waveform derived from rib cage motion and abdominal motion measured by external respiratory measuring devices, such as those based on inductive plethysmography, the measured respiratory drive being usable to initiate inspiration by a mechanical ventilator and for determining an index describing a shape of the waveform for controlling a continuous positive air pressure (CPAP) device.
(19) The '203 patent: U.S. Pat. No. 6,047,203, issued Apr. 4, 2000 and titled “Physiologic Signs Feedback System,” discloses a non-invasive physiologic signs monitoring device which includes a garment, in a preferred embodiment, a shirt, with electrocardiogram electrodes and various inductive plethysmographic sensors sewn, embroidered, embedded, or otherwise attached to the garment with an adhesive, signals generated by the sensors being transmitted to a recording/alarm device where they are logged and monitored for adverse or other preprogrammed conditions, which is signaled by When an adverse condition or other preprogrammed condition occurs, a message is communicated to the patient by either an audio message or a display. The recording/alarm unit is also connectable to a remote receiving unit for monitoring by a healthcare professional or other machine.
However, nowhere in the art of inductive plethysmography are found teachings of practical and effective apparatus for non-invasive, ambulatory monitoring, of pulmonary and cardiac parameters. Such practical and effective monitoring apparatus would be of great benefit by assisting the transfer of health care from traditional hospital-based care, which is administered by trained health care workers, to home-based self care, which is administered by the individual patient during, if possible, the patient's normal daily activities. This transfer in health care has been found socially desirable because it may reduce health care costs and may increase patient involvement in and commitment to their treatment plans. Non-invasive and ambulatory monitoring apparatus may assist this transfer, because it eliminates the risks associated with invasive sensors placed within the body, such as intravascular catheters, risks which are considerably heightened outside of the hospital.
Citation or identification of any reference in this Section, including the patents listed above, or in any section of this application shall not be construed that such reference is available as prior art to the present invention.